Study On The Water Conservation Forest And Its Function Assessment In Datong County

The Beichuan River and the Heiquan Reservoir is the main water resource of the region around Xinning. The Picea crassifolia has been chosen to be the main species of water conservation forest. But the water conservation ability of Picea crassifolia forest and other main vegetation types are unclear. On the basis of site type division, this paper has figured out the relative water conservation ability of each stand through the research on canopy, litter and soil of each stand when there was no runoff data. The afforestation regions of each vegetation type were figured out by comparing the distribution regions with the regions where these vegetation types give the best water conservation ability. Furthermore, the paper analyzed the changing of water storage capacity of soil in Datong County after afforestation. The research intended to provide some theory support on the managements of water conservation forest in Datong County. The main achievements of this paper were as follows:(1) On the basis of former site type division, this paper took the elevation, aspect, slope and soil thickness as the main natural environmental factors, combined with the vegetation survey result, the region of Datong County was divided into 21 kinds of site types. There are 8 kind of water conservation forests in Datong county, those are Betula platyphylla, Larix principis-rupprechi, Populus cathayana, Picea crassifolia, Hippophae rhamnoides subsp. Sinensis, Picea crassifolia×Betula platyphylla, Picea crassifolia×Larix principis-rupprechi and shrubs. These forests mainly distribute in the site types of flood plain, river terrace, low-hill shady gentle slope with deep soil, low-hill sunny gentle slope with deep soil, low-remote-hill shady gentle slope, low-remote-hill shady precipitous slope, low-remote-hill sunny gentle slope, low-remote-hill sunny precipitous slope, low-remote-hill shady gentle slope, low-remote-hill shady precipitous slope, low-remote-hill sunny gentle slope and low-remote-hill sunny precipitous slope.(2) Main factors which affected the water conservation ability of canopy were the canopy height, gap fraction and canopy storage capacity. The main factors which affected the water conservation ability of litter were the thickness, reserve, interception ability (the sum of the saturated water storage capacity of non-decomposed layer and the absorbed water storage capacity of semi-decomposed layer) and absorption ability (the sum of absorbed water storage capacity of the non-decomposed layer and the semi-decomposed layer). The main factors which affected the water conservation ability of soil were the capillary porosity, non-capillary porosity and saturated hydraulic conductivity within the depth of 0-60 cm and 0-20 cm.(3) Vegetation type which gave the best water conservation ability on each site type were:flood plain----Populus cathayana, river terrace----Populus cathayana, low-hill shady gentle slope with deep soil----Picea crassifolia, low-hill sunny gentle slope with deep soil----Picea crassifolia, low-remote-hill shady gentle slope----Betula platyphylla, low-remote-hill shady precipitous slope----Betula platyphylla, low-remote-hill sunny gentle slope----shrubs, low-remote-hill sunny precipitous slope----shrubs, middle-remote-hill shady gentle slope----Betula platyphylla, middle-remote-hill shady precipitous slope----Betula platyphylla, middle-remote-hill sunny gentle slope----shrubs, middle-remote-hill sunny precipitous slope----shrubs.(4) The research figured out that areas of Betula platyphylla, Populus cathayana, Picea crassifolia, shrubs and sparse vegetation would be 206.93 km2,10.63 km2,69.91 km2,508.76 km2 and 697.53 km2 after afforestation, respectively. The area of shrubs and sparse vegetation would decrease by 170.19 km2 and 27.47 km2 after afforestation, respectively. The capillary soil storage capacity would increase by 1.62×107 m3. The non-capillary soil storage capacity would increase by 1.30×106 m3. The saturated soil storage capacity would increase by 1.75x107 m3. The values of the increased water conservation function base on the increase of the saturated soil storage capacity and the non-capillary soil storage capacity would be ￥74,920,000 and ￥5,530,000, respectively.